1. Field of the Invention
This invention relates to a group of pharmaceutically acceptable amino-carboxylic acids and their amide derivatives and to pharmaceutical uses for these compounds. More particularly the invention pertains to the use of these compounds as anti-convulsant, sedative and anxiolytic agents in mammals.
2. Description of the Prior Art
Certain induced, recurrent, generalized seizures in mammals can be prevented by the administration of glutamine (GLN). These seizures have been thought to be related to the depletion of brain glutamine and its product gamma-amino-butyric acid (GABA), which is known to be a major inhibitory neurotransmitter substance acting between the nerve cells in the brain. Decreased GABA in the brain causes seizures. A precursor of GABA is the amino acid glutamine. GABA itself cannot be used clinically to prevent seizures because it does not cross the blood-brain barrier and has serious side effects (hypotension, shock, mortality). Glutamine is metabolized too quickly to be pharmacologically effective.
Several investigators have indicated that the use of GABA agonists given systemically is not associated with a useful anti-convulsant effect. For example, Meldrum (in an article published in The Lancet, August 5, 1978, at p.304-306) teaches that diffuse activation of GABA receptors by GABA or a GABA agnoist given systemically does not provide a useful anti-convulsant effect. An article by Tsuchiya et.al., in Journal of the Physiological Society of Japan, 22,70-74 (1960) reports on the administration to mice of GABA and delta-amino valeric acid (DAVA) ten minutes before inducing convulsions by the application of electroconvulsive shock. The results reported by the authors demonstrate that DAVA is ineffective in preventing or inhibiting convulsions and after initial testing the compound was dropped from subsequent anticonvulsant trials as reported in the article.
It has now been unexpectedly discovered that DAVA's anticonvulsant activity is delayed after introduction and administration of DAVA and other related amino-carboxylic acids either as free amino acids or their amide derivatives can be used to prevent seizures in mammals or decrease the severity of convulsive episodes.
It has also been surprisingly found that these amino acid components are useful an anxiolytic agents in mammals.
Accordingly, it is an object of the present invention to provide a method of preventing seizures, and particularly epileptic seizures in mammals.
Another object of the present invention is to provide pharmaceutical dosage forms containing amino acid compositions which are analogs of glutamine, thus making more glutamine available for conversion to GABA.
Still another object of the present invention is to provide pharmaceutical formulations comprising an effective amount for inhibiting the onset of seizures of an amino acid composition in a solid or liquid dosage form.
A further object of the present invention is to provide an effective method of administering the anti-convulsant compositions disclosed herein.
A further aspect of the present invention is to provide effective sedative compositions.
These and other aspects of the invention will be apparent from the following description.
Convulsive disorders (e.g. epilepsy, seizures, fits, convulsions) have in common the occurrence of brief episodes. These episodes are associated with loss or disturbance of consciousness. Such episodes are usually but not always associated with characteristic body movements, and sometimes with autonomic hyperactivity. They are generally correlated with abnormal EEG discharges. The etiology of such disorders is varied and includes, e.g., genetic diseases, metabolic dysfunction, tumors and trauma.
The amino acids found to be useful as anti-convulsant and anxiolytic agents in the present invention may be generally described as aliphatic compounds in which the carboxylic acid and primary amine are separated by three or four units constituting a simple or substituted alkane, an ether or thioether, or an amide forming the backbone of a straight or branched chain molecule. The amine and carboxylic acid are either free acids or an amide and/or ester derivative of the acid. The amide and ester forms have been found to facilitate entry of the compound into the brain.
The active compositions of the present invention are represented by the following general formula: ##STR1## wherein
R.sub.1 is H, ##STR2##
A is H, Ch.sub.3, CH.sub.3 CH.sub.2 --, HO--CH.sub.2, HO--CH.sub.2 CH.sub.2, CH.sub.3 OCH.sub.2 -- HS--CH.sub.2 --, HS--CH.sub.2 CH.sub.2 --, CH.sub.3 SCH.sub.2 --,
Y is C.dbd.O, HC--OH or, CH--A,
Z is CH--A, O, S; or NH only if Y is C.dbd.O, and
R.sub.2 is --OH, --NH.sub.2 or CH.sub.3 --CH.sub.2 --O--,
N is 0 or 1, and Y is CH--A when N.dbd.O; and
A+Y+Z include no more than one Oxygen or Sulfur atom
The preferred anti-convulsant of the present invention is DAVA or delta aminovaleric (5-aminopentanoic) acid of the formula: ##STR3##
Aside from its anxiolytic and anticonvulsant activity, DAVA and other compounds of the general formula have been found to posess sedative properties when administered in effective amounts for this purpose.
In administering DAVA and the other compositions of the inventin it has been found desirable to reduce their acidity by buffering them to between about pH 4.0 to about pH 6.8. Preferably the present compositions are buffered to pH 4.5. This buffering action can be achieved by co-administering DAVA or the other active agents with a pharmaceutically acceptable organic or inorganic buffering agent. Illustrative buffering agents for the present invention include calcium citrate, calcium carbonate, aluminum hydroxide, sodium bicarbonate, magnesium oxide, magnesium carbonate and sodium carbonate.
In considering the substituents of the general formula described above it has been noted that only a single oxygen or sulfur atom is present in A, Y and Z. The preferred constituent of the R.sub.1 group is hydrogen although acetyl ##STR4## is also desirable at this position. Besides the R.sub.1 groups shown to be useful in the general formula, acyl groups derived from other simple metabolizable organic acids such as, citric, or butyric acid have been found useful.
As constituent A of the general formula hydrogen is the preferred moiety. However, compounds in which A is a CH.sub.2 --OH group have been found to perform almost as well as those which contain the H moiety.
In addition to the moieties enumerated in the general A formula set forth above, anxiolytic and anticonvulsant activity has also been found in compounds of the general formula wherein the A constituent is selected from groups having homologous side chains with 3 or 4 carbons in a straight or branched chain configuration. Representative of this class of constituents is 5-amino-4 hydroxy octanoic acid.
The preferred constituents of the Y and Z groups is CH.sub.2, which is especially preferred. As to the Z groups, it should be noted that NH may only be present at this position when the Y constituent is &gt;C.dbd.O.
Hydroxy (--OH) is the especially preferred constituent at the R.sub.2 position in the general formula for the present pharmaceutical compounds, although amino (--NH.sub.2) is also a preferred R.sub.2 constituent. Compounds in which other esters and amides (e.g. peptides) are constituent R.sub.2 have shown some anticonvulsant activity, but are not believed to offer any particular benefit or advantage over those in the general formula.
In addition to DAVA, the preferred compound of the present invention, 5-amino-4-oxo-pentanoic acid, 2-aminoethoxy acetic acid, 2-aminoethylthio acetic acid, and 5-amino-4-hydroxy pentanoic acid, also display anticonvulsant and anxiolytic properties in animals.
Although principal use of the compounds of the invention is anticipated to be as oral or parenterally administered pharmaceutical agents for prevention, inhibition or arrest of epileptic discharges in humans, the desirable sedative properties of DAVA are also of great significance. This is particularly true in view of the relatively non-toxic nature of the present compounds and the fact that they may be synthesized at relatively low cost.
The compositions of the present invention are preferably administered via the oral route, although parenteral administration by subcutaneous, intramuscular annd intravenous injection is also effective. The oral dose may take the form of a tablet, capsule, pill, beadlet or other solid dosage unit. The active ingredients may be compounded in the desired oral form in combination with inert ingredients including fillers such as talc, lactose, starch, bentonite and diatomaceous earth; lubricants and food flavorings.
Liquid oral doses in the form of solutions, and suspensions are also contemplated by the invention. For parenteral administration the compounds of the invention are preferably dissolved in distilled water, isotonic saline solution or any other pharmaceutically acceptable carrier liquid.
Several of the (4-) and (5-) amino carboxylic acid compounds in this series are commercially available. They include among others, 5-aminopentanoic acid, 5-aminolevulinic acid, and glycylglycine, all available from Sigma Chemical Company, St. Louis, Mo.
The other compounds of the general formula can be directly prepared by conventional synthetic procedures or using processes described in the literature. Thus, 2-aminoethoxy-acetic acid may be prepared according to the synthesis taught in Acadamie des Sciences, Paris. Comptes Rendus Hebdomadaires des Seances (Compt. Rend.) 234, 1980 (1952), CA 47,2761e. 5-amino-hexanoic acid can be synthesized by the method in Ricerca Scientifica 1, IIA, 312 (1961), CA57,9658h. 5-amino-4-hydroxy-pentanoic acid is prepared by reduction of 5-aminoevulinic acid using the procedure taught in Biochemical Biophysical Research Communications 39, 135 (1970); and 4-amino-5-hydroxy-pentanoic acid, synthesized by the method in Biochemica Biophysica Acta 8, 287 (1952), CA 47, 4843d. Other compounds of the invention such as 2-acetoxy-1-propylamine, 1-acetoxy-2-propylamine, 2-acetoxy-1-butylamine, 1 acetoxy-2 butylamine and 2-amino-ethylthio-acetic acid are prepared by adaptation of the method for preparing 2-amino ethoxyacetic acid (taught in the Compt. Rend. article referred to above) by substituting, respectively, in the synthesis of each of the above amino acids: 1-amino-2-propanol, 2-amino-1-propanol, 1-amino-2-butanol, 2-amino-1-butanol and 2-amino-ethylthiol.
It is to be understood that where an amino acid compound described in the art is identical with one of the above specified named compounds, but has been known by another name by reason of isomerization or production in accompaniment with other compounds, the identification of such substances by the name set forth above is intended to identify the same compound under all other designations.
When used as anticonvulsant agents in mammals, the present compositions are administered at a dosage level of from about 0.03 to about 50 mmol of active ingredient per kilogram of body weight. For parenteral administration the compounds of the invention are desirably administered in a 1.5 M solution in isotonic (normal) saline. The daily effective dosage, or the dosage required to prevent or inhibit convulsions from a particular disease or stimulus depends upon the condition being treated, the individual characteristics of each mammal being treated and the nature of the physical or chemical stimulus inducing or responsible for the convulsive activity. Thus, the exact dose required to alleviate convulsions attributable to a particular disorder or stimulus will vary from one patient to another. The anxiolytic properties of the present compounds are evident in the same dosage ranges employed for anticonvulsant treatment. Sedative properties of the present agents are apparent at approximately twice the anti-convulsant dosages, i.e., dosages of between about 0.06 and 100 mmol active ingredient per kilogram of body weight are sedative dosages.
Solid pharmaceutical dosage forms such as pills, capsules, and tablets may contain from 5 to about 750 milligrams of active ingredient. Preferably from about 50 to about 500 milligrams of active ingredient is incorporated in each solid dosage form together with the required amount of buffering compound to bring the pH of the dosage unit to about 4.5.
The liquid dosage forms of the present invention are preferably administered in the form of a solution or suspension in a pharmaceutically acceptable vehicle, preferably distilled water. Liquid dosages containing from about 5-100 milligrams of active ingredient per cubic centimeter of vehicle have been found to be useful in administering these agents to mammals. The preferred concentration within this range will depend upon the age and weight of the subject being treated.
It is also contemplated that the anti-convulsant agents of the invention may be administered in the form of rectal suppositories. Suitable suppository dosage forms may be prepared by incorporating the active agent into a shapeable base material. Among the suppository bases that can be used to prepare suppositories according to the present invention are cocoa butter, glycerinated gelatin, hydrogenated vegetable oils, mixtures of polyethylene glycols of various molecular weights, and fatty acid esters of polyethylene glycol. Rectal suppositories for adults are tapered at one end, usually weigh about 2-4 grams and may contain from about 5 to about 500 milligrams of active ingredient. Preferably such suppositories are made from one or more bases having a melting point that will enable them to melt or dissolve slowly upon retention in the rectal cavity.
The anticonvulsant activity of the instant aminocarboxylic acid compounds was measured against seizures produced in female DBA/2J mice using: L-methionine-RS-sulfoximine (MSO), 100 mg/Kg injected subcutaneously (SC), pentylenetetrazole (PTZ), 65 mg/Kg, SC or electroconvulsive shock (ECS), 18 mA at 380 V for 0.1 sec. These are standard test conditions which produce convulsions in 90-100% of saline injected (control) animals.
In testing representative compounds of the invention for anti-convulsant activity Glycylglycine (Glygly), Glycine (Gly), Glutamine (Gln), 5-amino-valeric acid (DAVA) and 5-amino-levulinic acid (DALA) were administered to the DBA/2J animals SC at 15 mmol/kg body weight or orally at 30 mmol/kg of body weight. The active ingredients were injected or administered 45 minutes after MSO injection or 60 minutes before PTZ or ECS administration. Saline injected controls were treated in parallel with those animals receiving an active dose. In some instances glygly injected animals and saline controls were given ECS after 180 minutes.
An important aspect of the present invention involves administration of the active anti-convulsant substantially prior to the application or onset of the convulsive stimulus or attack. Generally the active agent should be administered from at least 30 minutes to 4 hours or more before application or onset of the seizure stimuli whose inhibition is sought. The interval between administration of the agent and observation of its anticonvulsant effect is believed to be attributable to the fact that the mode of action of these agents is to spare glutamine, a GABA precursor, thus making more Glutamine available for the production of GABA. During this latency, the glutamine which has been spared must travel to the pre-synaptic terminals of the neurons where it is metabolized to GABA. Glutamine also plays an important role in other metabolic processes in the brain. Thus, the mechanism of action of the active compounds in the present invention is believed to be different than for prior art anticonvulsant agents which directly affect the ability of the synapses to transmit neural impulses.
For administration via the parenteral route in mice, the acid compounds of the invention were injected subcutaneously, in isotonic saline solution, at a dose of 15 mmol/KG body weight. Anti-convulsant activity against seizures produced by MSO or PTZ was determined by measuring the difference in time to onset of seizures between experimentally treated animals and saline injected control animals. The effectiveness against ECS seizures was measured on a four point scale with seizure severity being scored as follows: Seizure with full extension and death, 3; seizure with full extension, 2; clonic seizure without tonic extension, 1; no seizure, 0.